1. Field of the Invention
The present invention relates to novel conductive barrier structures useful in integrated circuit memory cells, integrated capacitors for decoupling, integrated RC-matching networks or other electronic devices requiring high specific capacitance. In specific aspects, the present invention relates to microelectronic structures, e.g. including such conductive barrier layers between complex metal oxides of high dielectric constant and respective Cu or Al electrodes.
2. Description of the Related Art
Barrier layers are crucial components in many integrated circuits. Barrier layers are typically used to prevent interfacial diffusion of oxidizing species, silicon, metals, hydrogen, etc., while concurrently maintaining desired conductance/resistance characteristics in the integrated circuit structure.
Integrated circuit memory devices, such as dynamic random access memories (DRAMs), include storage cells comprising transfer transistors and capacitors, for temporarily storing information. There has been continuing improvement in IC devices with respect to the number of storage cells per device, for many years. Each increase of storage capacity is made possible by shrinking the amount of space, ( i.e., the device surface area, occupied by each storage cell) by corresponding reduction of the size of its storage cell components.
In memory cells of such type, capacitance of the capacitor is particularly important since the capacitor”s ability to accurately store and “read out” bits of data is closely related to the quantity of charge that is able to be stored in the capacitor. In the past, capacitance has been kept high by forming three-dimensional capacitors such as trench capacitors and stacked capacitors. More recently, circuit designers have pursued capacitor structures including an insulator material with a high dielectric constant. High dielectric constant materials have been employed, having a dielectric constant much higher than the dielectric constant of such familiar materials as silicon dioxide (SiO2) and silicon nitride (Si3N4).
Other applications of integrated capacitors also require higher capacitance and, by extension require higher dielectric constant materials as the dielectric layer. These applications include high performance decoupling capacitors, integrated RC (impedance) matching networks, other analog applications, and active circuit elements including electrically tunable capacitors, IR detectors, sensors, micromechanical machines and other more exotic circuit applications.
Commonly used high dielectric constant materials include complex metal oxides such as SrBi2Ta2O9 (SBT), (Ba,Sr)TiO3 (BST), and Pb(Zr,Ti)O3 (PZT). It is well known that the optimal performance of these materials requires electrodes made from noble metals (i.e., Au and Pt), noble metal alloys, or oxides such as RuO2, etc.
In addition, other intermediate dielectric constant materials such as Ta2O5 and alloys of tantalum and niobium oxides with other transition metal oxides can produce capacitors on non-noble metal electrodes, but like the high dielectric materials, their performance is optimized by the use of noble metal or noble metal oxide electrodes.
Noble metal electrodes possess many important physical or chemical characteristics, such as high oxidation resistance, high work function (providing reliable low leakage), a propensity to cause high dielectric constant oxides to crystallize easily on them, and high temperature stability. These characteristics are particularly crucial for bottom electrodes, which must withstand the stress of high temperature and oxidizing conditions during chemical vapor deposition (CVD) of high dielectric constant thin films thereon.
Unfortunately, such noble metals, noble metal alloys and oxides are very expensive and of limited availability for use in semiconductor production environments.
Moreover, such materials are very difficult to etch or to polish, and they require etching or polishing compositions of very strong acidity or corrositivity. Handling compositions of such strong acidity or corrositivity in turn increases the operating costs of the semiconductor manufacturing facility. Discharge of such etching or polishing compositions after the semiconductor manufacturing process also leads to significant environmental problems and/or treatment costs.
Further, such noble metals, alloys, and oxides, especially Pt and Pt alloys, have relatively low conductivity.
In view of the shortcomings of the above-described electrode materials of construction, aluminum and copper have come into usage as alternative electrode materials. Aluminum and copper have reduced cost compared to noble metals, and they have excellent conductivity.
However, both aluminum and copper have relatively high oxidization potentials and low oxidization resistances. They also are subject to rapid oxidization in a high-temperature, oxidizing environment. This in turn has adverse implications for the conventional method of forming the high dielectric constant oxide material, chemical vapor deposition (CVD). Chemical vapor deposition of complex metal oxides thin films of high dielectric constant (k) is generally carried out in an oxidizing environment under elevated deposition temperatures to ensure good crystallinity and electronic properties of such films. Electrodes comprising aluminum or copper cannot maintain their integrity under such chemical vapor deposition processes. This circumstance renders it difficult to use aluminum or copper electrodes in combination with high k metal oxide thin films.
Further, even without exposure to the chemical vapor deposition process, aluminum or copper is still susceptible to being oxidized at the Cu,Al/high k metal oxide interface, by oxygen diffusion through such interface. The resultant generation of Cu oxides or Al oxides roughens the Cu,Al/high k metal oxide interface and changes local electrical properties at or near the interface. Typical electrical property changes include, but are not limited to, increased leakage and energy loss. Severe leakage and energy loss will in turn cause catastrophic breakdown (i.e., a short-circuit) between the electrodes and render the capacitor useless.
The present invention therefore relates to use of various barrier layers between the complex metal oxides of high dielectric constant and the Cu or Al electrodes, to avoid the above-discussed problems.